1. Field of the Invention
The present invention relates to a current sensor that has high accuracy and low power consumption over a wide measuring range.
2. Description of the Related Art
For example, the magnitude of a current for driving a motor of an electric vehicle or a hybrid car (combination of electricity and gasoline) is measured by a current sensor. In addition, even in a battery for driving a motor, a battery residual amount is managed by detecting an amount of a current flowing into and out of the battery using the current sensor. A magnetic proportional current sensor and a magnetic balance current sensor may be given as examples of the current sensor. In the magnetic proportional current sensor, a magnetic field proportional to a current to be measured passes through a core gap by a magnetic force line generated within a magnetic core, and the magnetic field is converted into a voltage signal by a magnetic detecting element, thereby generating an output voltage proportional to the current to be measured. Meanwhile, in the magnetic balance current sensor, when the current to be measured flows, an output voltage is generated in the magnetic detecting element by a magnetic field corresponding to the current, and a voltage signal output from the magnetic detecting element is converted into a current to thereby be fed back to a feedback coil. As for the magnetic balance current sensor, the magnetic field (a cancellation magnetic field) generated by the feedback coil and the magnetic field generated by the current to be measured are canceled out from each other, and therefore the magnetic balance current sensor is operated so that the magnetic field is always zero. In this instance, a feedback current flowing in the feedback coil is subjected to voltage-conversion to thereby obtain the voltage-converted current as an output.
As the magnetic detecting element in the current sensor, a magnetoresistance effect element such as a Hall element or a giant magneto resistance (GMR) element may be used. In the magnetic proportional current sensor using a Hall element as the magnetic detecting element, in a case in which a measurement range is widened, resolution is decreased when the current to be measured is small. In the magnetic balance current sensor using the Hall element as the magnetic detecting element, a magnetic field due to a large current cannot be canceled. Therefore, in Japanese Unexamined Patent Application Publication No-2007-78416 as a method for compensating the both problems, a method, in which the magnetic proportional current sensor using the Hall element and the magnetic balance current sensor using the Hall element are disposed, and these are switched to be used according to the magnitude of the current to be measured, is disclosed.
However, in the magnetic current sensor such as the magnetic balance current sensor or the magnetic proportional current sensor, a measurement range is limited by various conditions such as magnetic saturation, a power supply voltage. Therefore, when the current to be measured is measured using the magnetic current sensor, the use of the magnetic current sensor is limited within the measurement range. In the technology disclosed in Japanese Unexamined Patent Application Publication No-2007-78416, the magnetic proportional current sensor is used in a large current area, but the use of the magnetic proportional current sensor is limited to a range that is not magnetically saturated, and therefore the measurement range cannot be widened. In addition, in the technology disclosed in Japanese Unexamined Patent Application Publication No-2007-78416, two types of current sensors should be separately prepared. Therefore, space saving cannot be achieved and a manufacturing process becomes complex.